1. Field of the Invention
The present invention relates to devices for detecting radiation, particularly to devices for determining skin-damaging levels of ultraviolet (UV) radiation.
2. Description of Prior Art
Solar radiation reaching the earth consists of electromagnetic energy ranging from ultraviolet (UV) light to infrared (IR) light. UV radiation is further subdivided into three types: UV-A, UV-B, and UV-C. UV-C radiation has wavelengths in the range of 200 to 285 nanometers (nm) and is totally absorbed by the earth's atmosphere. UV-B, from about 285 to 318 nm, is known to cause skin cancer in humans. UV-A, from about 315 to 400 nm, is mostly responsible for tanning. However, UV-A has also been found to play some role in skin cancer and is the cause of eye cataracts, solar retinitis, and corneal dystrophies.
Based on general principles and techniques for radiometry and photometry, several UV radiation-measuring and warning instruments have been developed and made commercially available.
A personal UV radiometer, described in U.S. Pat. No. 5,008,548 to Nahum Gat, 1991, includes an LCD display, a photocell, and an integrated circuit for processing user inputs and UV radiation data.
However, this radiometer is unable to correctly monitor levels of UV radiation when it is not directly exposed to solar rays, i.e., when it is placed in the shade. Moreover, the device does not take into account the changes in skin pigmentation which occur while a person is being exposed to solar radiation. Furthermore, this device is not maximally convenient, since it is intended for attachment to an article of clothing and may restrict movement of a person during rigorous physical activity, for instance, a volleyball game.
An apparatus, disclosed in U.S. Pat. No. 4,985,632 to Frank Bianco et al., 1991, comprises an electronic wristwatch having a digital readout for displaying the time, the day, and the month. It also incorporates a photodiode for detecting skin-damaging UV radiation, a microcomputer, and four function buttons.
This device, however, is not user-friendly due to its large number of functions, many of which are superfluous. Moreover, like the radiometer, the wristwatch does not take into account skin pigmentation changes which occur during exposure to UV radiation. Furthermore, it can not monitor UV radiation when placed in the shade.
All of the above the prior-art devices are based on the assumption that the amount of UV radiation that may be safely tolerated by human skin is independent of the intensity of incident radiation and is determined only by the total accumulated energy. Even though some prior-art devices directly measure the intensity level of incident radiation, this measurement is not factored into the calculation of a safe UV-energy threshold.
In other words, none of the prior-art devices are able to predict the effects of a given radiation dose received at different rates by a subject's skin. As illustrated in FIGS. 1A and 1B, total accumulated energy quantities E.sub.1 and E.sub.2 are represented as areas under intensity versus time curves and are numerically equal. However, a subject who absorbs energy quantity E.sub.2 is much more likely to suffer from harmful effects of UV radiation (sunburn, eye irritation, etc.) than a subject who receives energy quantity E.sub.1, since energy quantity E.sub.2 is more intense and has been absorbed over a much shorter period.